WRAPUP 8-Democrats Obama, Clinton ready for long battle

(adds Washington Post-ABC News poll)

By John Whitesides, Political Correspondent

WASHINGTON, March 5 (Reuters) - Barack Obama and Hillary Clinton on Wednesday faced a long fight for the Democratic U.S. presidential nomination, with Obama promising to get tougher on his rival and Clinton hinting the two could team up in November against Republican John McCain.

McCain won the endorsement of President George W. Bush in a White House ceremony that capped the Arizona senator's rise to the party's nomination after his campaign nearly collapsed last year.

While McCain turned his attention to the November election, Democrats faced more of the grueling state-by-state nominating duel between Obama and Clinton that threatened to extend into June or beyond.

Clinton dodged another possible knockout blow from Obama on Tuesday, coming back from a series of losses to win the big states of Ohio and Texas and revitalize her campaign. The New York senator said the wins showed she had the type of broad support needed against McCain.

Obama promised to more aggressively confront Clinton, who hammered him in Ohio and Texas with questions about his readiness to be commander in chief, his commitment to renegotiating U.S. trade deals and his strength in a general election campaign.

"I think that over the coming weeks we will join her in that argument," Obama told reporters. "She has made the argument that she is thoroughly vetted, in contrast to me. I think it's important to examine that argument."

His campaign renewed demands that Clinton release tax returns filed with her husband, former President Bill Clinton, since they left the White House. Clinton aides said she would release the returns "on or around April 15."